I've not used nor touched KerdiBoard, so have no input, one way or the other. But, if you read the installation instructions, all seams and joints or penetrations are required to be waterproofed, either by the standard minimum 2" overlap with fabric (band or sheet material) and the penetrations with the gaskets or KerdiFix. Done this way, no water should penetrate, and thus, the problem should go away. Working with any of these materials, good workmanship is the key to success - any system can fail if you do not follow all of the instructions.

The tech sheet says ALL penetrations need either one of their seals, or KerdiFix to ensure there is no chance of moisture getting inside of the board. Normal joints/seams require the same thing as Kerdi sheet membrane - a minimum of 2" overlap of material with an unmodified thinset bonding. The inside of the shower/steam room, when using KerdiBoard must be made waterproof and penetrations properly sealed to prevent moisture or vapor from intruding into the system. As I said, I have neither touched nor seen KerdiBoard, and other than the tech sheets, I don't know any more about it.

For others that may read this, the shower in question is a commercial steam room, likely run many hours a day. From what I read, Schluter is on site trying to help understand what went wrong and how to fix it as any of the quality companies out there typically do when there's an issue if you contact them.

Let's not come to a conclusion until more is known.

A typical home steam shower is used probably less than an hour a day, if that, giving the whole thing a chance to dry out if vapor did get places you'd rather not get it. Schluter does not approve of gypsum based backers for commercial steam showers (per their Kerdi shower handbook installation instructions) that are likely to be used much more than that. No membrane is 100% given high steam concentrations, and an inert backer is required when it is likely it will have minimal chance to dry after long-term, continuous high vapor pressure exposures of a commercial operation. For a home, a typical steam shower use probably isn't worse than a typical teenager's long, use all the hot water shower, and for those applications, accepts the use of numerous backer materials since there's typically a large percentage of the day when it is unused and drying.

One thing to consider, steam can get VERY hot, just like any gas. While there's a limit on how hot liquid water can get unless under pressure, there's no such limitation once it becomes a gas. There's no way to know what temp the steam was in that system that could have been run 24/7, and the steam line ran, uninsulated for the most part, right behind the board. A typical home steam shower, the pipe comes straight into the shower, and doesn't run long distances against the backer , entering at a 90-degree angle with minimal contact with the backer, keeping the run short to maximize the effect and efficiency of the system. A commercial system could be feeding multiple shower rooms, and would likely run hotter and would need to be piped further.

The steam line should be insulated. It should not be in direct contact with the material. This is for two reasons: to keep the line hot possibly making the surface dangerously hot to occupants, and to preserve the material. A steam line run in direct contact with any surface that is tiled could put some really bad stresses on the ceramic or stone tile on the surface - especially in a commercial steam room that may run extended hours. It could get hot enough to burn someone and be a safety hazard as well.

Steam is the vapor created by boiling water. Water boils at 212 at sea level. Steam CAN be significantly hotter. Since it originated from boiling water, which was 212, on the outlet to only be 110, most of it would have condensed, and you won't have much steam...saturated air, certainly, but not steam. So, you could have lots of heated mist at 110, but not steam. The mist is liquid droplets of water, steam is a colorless vapor. The mist forms when the steam hits the cooler air of the steam room. So, how does a steam generator making at least 212-degree steam vapor at the source, ensure it is only 110 at the outlet?

The foam won't melt at 212, but the rest of the structure might have problems. I did find in the spec sheet a maximum of 158-degrees F - missed that the first time through.

No idea how hot the actual steam pipe got, but it wouldn't surprise me if it exceeded that if ran uninsulated against the back. Depending on where the steam generator is located, it's likely to exceed that for at least some of the run, if not all.

Everyone that has common sense knows that a paper based products are inferior to a cement product. Mr.Whipple........it is very difficult to defeat "stupid".....I have defeated it in the past but it takes many posts......as your finding out.

Since I've never seen Kerdiboard except in pictures, I don't know if it has a code stamped on it like some food products, or other items for batch control. If it does have a printed number on it, the manufacturer would probably know how to decode it.

The stupidest I have ever seen are women managers, those, in jobs, where an education is not necessary and they thrive on what they seemingly see, as power. They fear losing it for then, they go back to flipping burgers. Might be the same for men managers, but, I know for sure, it is with women. Those with the least amount of education has the most need to prove their self-worth in their job.

This is why I stay in the man's world, women on the whole has not evolved enough for me.

Those are words spoken in truth. I am 58 years old, have worked a lifetime in various positions ( ones needing education & diplomas, and then, others you just got to show up) and given a choice of the sexes to work with or for, I definitely, would pick the males.

Oh, and your comment about they would slap you upside the head? That is my point.

This is basically very true,
"Strange as it may seem, no amount of learning can cure stupidity, and formal education positively fortifies it."
Stephen Vizinczey